Ingition device for electric discharge apparatus



Nov. 25; 1947. A. GAUDENZIC IGNXTION DEVICE FOR ELECTRIC DISCHARGEAPPARATUS Filed May 16, 1944 Patented Nov. 25, 1947 UNITED STATESIGNITION DEVICE FOR ELECTRIC DISCHARGE APPARATUS Arthur Gaudenzi,

12 Claims.

less power and in addition possess a number of other advantages. Whenback-arcing occurs the igniter can be disconnected and re-ignitionprevented, whereupon the back-arc extinguishes. With this kind ofigniter the magnitude of the rectified voltage can also be regulated.The single anode valve with a periodically operating igniter does notrequire a cathode insulator, so that the cathode can be galvanicallyconnected with the casing. The cathode spots which occur after ignitionoriginate for instance at the centre of the vessel and during a halfwave never reach the wall of the vessel if the cathode diameter isgreater than about 200 millimetres. This is due to the fact that theradius of action of the cathode spots is less than 100 mm. during /100second.

Various kinds of periodically operating igniters are already known. Thebest known type is the semi-conductor igniter. It possess thedisadvantage, however, that during the course of time its propertieschange and as a result ignition failures occur, until finally theigniter fails to operate at all. Although various improvements have beenproposed and attempts have even been made to regenerate the igniterduring service or whilst operation is interrupted, all these endeavourshave failed to produce the desired results.

lhe present invention concerns an ignition device for electric dischargeapparatus with fixed ignition anode and. liquid cathode, where theaforementioned disadvantages of the hitherto known periodicallyoperating ignition devices are avoided. This is achieved according tothe invention by forming a space over part of the cathode which isprovided with a heating device, an ignition anode being arranged in thisspace in such a manner that the distance between this ignition anode andthe cathode amounts to at least the free path of the electrons, so thata glow discharge is made possible at a considerably lower ignitionvoltage when main discharge space.

A special ignition space which is essentially separated from the maindischarge space, so that a vapour density can be produced in the formerwhilst in the main discharge space the compared with the Wettingen,Switzerland, assignor to Aktiengesellschaft Brown,

Boveri &

Switzerland May 31, 1943 mercury in the main discharge chamber.

vapour density remains very low, can be achieved in various ways, anumber of constructional examples of the invention being illustrated indiagrammatic form in Figs. 1-4 of the accompanying drawing, where eachfigure shows an ignition device in longitudinal section.

In Fig. 1 a sing1e-anode valve is shown, the main components of whichare the metallic casing I, anode plate 2, anode bushing 3, main anode 5and mercury cathode 5 which is not insulated from the casing. Main anode4 has a control grid l arranged in front of it, this grid being fixed inan anode sleeve 5. An ignition anode 8 made of metal is mounted by meansof the insulating tube 9 in the anode plate 2. This tube 9 whichsurrounds the ignition anode 3 dips with its lower funnel shaped endinto the cathode mercury 5 and is provided with a number of uniformlydistributed openings It which enable the mercury to flow into theignition space and at the same time allow the cathode spots to wanderout from the ignition An iron cap I2 is welded into the cathode plate H,this cap being enclosed concentrically by the insulating tube 9. On theatmospheric side a heating coil i3 is arranged inside cap l2 by means ofwhich the mercury inside the tube 9 is heated, so that mercury vapourrises therein and completely fills the space up to the vapour density inthe ignition space inside the insulating tube 9 thus becomes very highwhen compared with the vapour pressure in the main discharge spaceoutside the insulating tube 9,

.- where corresponding to the low temperature there is only a very lowresidual gas pressure. The distance between the ignition anode 8 and thesurface of the mercury cathode must be such that it is at least equal tothe free path of the electrons.

If a voltage supply amounting to a few kilovolts is now connected to theterminal [4 of the ignition anode 8 and the cathode 5, a powerful glowdischarge with small cathode spots on the mercury will occur in theignition space inside the insulating tube 9. As soon as the main anode 4is connected to a voltage of the same frequency an arc will be producedin the main discharge chamber. By means of the glow discharge in theignition space it is thus possible to ignite the main discharge areperiodically and very accurately. The glow igniter will operate evenwhen in a dirty condition and is not subject to any changes. Inside tube9 the current always remains small because as soon as the currentexceeds 50 amperes the cathode spot splits up into space onto thecathode ignition anode 8. The

a large number of smaller spots of which several within a very shortspace of time wander out on to the cathode in the main discharge space,their rate of movement being very rapid.

In such cases where very high anode voltages are employed it can happenthat even when the ignition is interrupted the heated cathode portioninside the insulating tube 9 still produces such a high vapour densitythat an arc occurs between the main anode 4 and the cathodeportion intube 9, this arc burning through the openings ID. This arc can, however,be easily prevented if a negative blocking voltage is applied to thecontrol grid 1 at the same time as the ignition anode 8 is disconnected.

The ignition device according to the invention can be constructed invarious difierent ways and is by no means confined to the constructionalform shown in Fig. 1. The insulating tube surrounding the ignition anodecan for instance be made in two parts, the lower part which dips intothe cathode mercury being loosely connected to the upper part. Fig. 2shows a modified form of the invention where there is no rigidconnection between the insulating tube 9 surrounding the ignition anode8 and the tube section l5 dipping into the mercury 5, The upper end l6of tube portion I5 is in the form of a cone which fits into acorresponding funnel-shaped opening ll in tube 9, whereby both conicalelements 5, I! are kept closed merely by the upward thrust exerted bythe mercury. The gap in the cone is thus kept well closed without therebeing a rigid joint, so that both parts 9 and [5 can readily be mutuallyadjusted to a slight extent. Reference numeral It indicates thecommunicating openings in the lower tube portion l5 which enable themercury and cathode spot to move about as required. The mercury insidethe heating space is in this case heated directly by means of a heatingrod l9 which is fixed inside a cap built into the cathode plate II andprojecting into the cathode mercury. The heating current passes up therod l9 and is conducted away by means of sleeve 2|. These elements aremade of a material which is not affected by the mercury and has a highspecific resistance, such as a chrome-nickel compound, whichcan bewelded to the iron so as to form a vacuum-tight joint. In the exampleshown in the figure the cathode is also provided with a water-coolingsystem which is located in the double bottom 22.

Another modified constructional form of the invention is shown in Fig.3. The insulating tube 9 which surrounds the ignition anode 8 does notdip into the cathode mercury 5 in this case, but is provided with afunnel-shaped extension located just over the surface of the mercury 5.Cap 28 which is built into the cathode plate H and contains a heatingcoil 21, is surrounded by a concentric cylinder 28 which extends beyondthe surface of the mercury and is provided with slots 29. The arecurrent of the main anode 4 can thus burn freely between the funnel-likeextension 25 and the mercury inside cylinder 28. At the same time therewill always be sufiicient vapor density in the ignition space insidetube 9 to enable ignition to be initiated at any time, on condition ofcourse that the cathode heating coil 21 is in operation. With thisarrangement the level of the mercury can fluctuate very considerablywithout the ignition being affected.

As a contrast to the arrangements already described where the ignitionanode is fixed to the node plate, Fig. 4 shows a constructional form ofsubmerged in the invention where the ignition anode is built into thecathode plate from the underside.

In Fig. 4 the ignition anode 30, which is surrounded by a concentricinsulating tube 3| and provided with a current lead 32, is built intothe cathode plate 33, the ignition device projecting into the mercury tosuch an extent that the glow discharge path between the ignition anode30 and cathode 31 is at least equal to the free path of the electrons.Ignition anode 39 is covered by a hood 34 of ceramic material or metalwhich extends down to cathode plate 33 and thus encloses part of thecathode mercury. The mercury inside hood 34 is heated by a heating coil35, and openings 36 are rovided in the hood to enable the mercury tocirculate and to allow the cathode spot to wander out of the ignitionspace. As soon as the heating for the ignition is switched on themercury inside hood 34 is heated and mercury vapour fills the spacebetween anode 3c and mercury 3i. By this means the necessary ignitionconditions are produced so that when a voltage is applied to theignition anode 30 a glow discharge is started between this latter andcathode El, whereupon the main arc can ignite.

The ignition device according to the invention, of which only a few ofthe many possible constructional forms have been described, satisfiesall the requirements which an igniter has to fulfill. Its constructionis very simple and the materials required for same can readily beobtained and do not change during service. The power required to operatethe igniter is very small. The mercury vapour which forms inside theignition space only escapes to a very slight extent into the maindischarge space. During pauses in the operation of the converter notmuch mercury vapour will condense on the anode. When adequate lateralheat insulation is provided very little heat will pass from the heatingdevice beneath the ignition space to the main mass of the cathodemercury. During longer interruptions in service the heating power can bereduced or completely switched on. All parts which are touched by thecathode spot must be highly heatresistant, so that it is an advantage tomake these elements of quartz or high quality glass.

Although the ignition device according to the invention has only beendescribed in connection with single anode-converters it can of coursealso be used with multi-anode converters. The ignition device can alsobe used in a known manner for the purpose of regulating the voltage whenthe required phase displacement between the ignition and main anodevoltage occurs. Furthermore by switching-off the ignition whenback-arcing occurs, it is possible to cause the back-arcing current tobecome extinguished.

I claim:

1. Electric discharge apparatus comprising, in combination, a mainanode, a cooperating liquid cathode, an ignition anode spaced from saidcathode a distance at least equal to the free path of the electrons,means providing a restricted space around said ignition anode, heatingmeans said liquid cathode and arranged and adapted to vaporize a portionthereof, and means for directing the vapor into said restricted spacewhereby a glow discharge results between said ignition anode and saidcathode on application thereto of predetermined voltage to initiatecurrent flow between said main anode and said cathode.

2. Electric discharge apparatus comprising, in combination, a mainanode, a cooperating liquid cathode, an ignition anode spaced from saidcathode a distance at least equal to the free path of the electrons,means providing a restricted space around said ignition anode, heatingmeans disposed entirely underneath the surface of said liquid cathodeand arranged and adapted to vaporize a portion thereof, and means fordirecting the vapor into said restricted space whereby a .glow dischargeresults between said ignition anode and said cathode on applicationthereto of predetermined voltage to initiate current flow between saidmain anode and said cathode.

3. Electric discharge apparatus comprising, in combination, a mainanode, a cooperating liquid cathode, an ignition anode spaced from saidcathode a distance at least equal to the free path of the electrons,means providing a restricted space around said ignition anode, heatingmeans disposed externally of said liquid cathode in heat transferrelation with the oathode to vaporize a portion thereof, and means fordirecting the vapor into said restricted space whereby a glow dischargeresults between said ignition anode and said cathode on applicationthereto of predetermined voltage to initiate current flow between saidmain anode and said cathode.

4. Electric discharge apparatus comprising, in combination, a closedcontainer, a main anode mounted on said container, a cooperating mercurycathode carried by said container, an ignition anode carried by saidcontainer and spaced from said cathode a distance at least equal to thefree paths of the electrons, closure means within said containerproviding a restricted space around said ignition anode, and heatingmeans disposed externally of said cathode in heat transfer relationtherewith to heat the portion of said mercury in closest proximity tosaid ignition electrode, whereby a glow discharge is caused therebetweenon application thereto of predetermined voltage to initiate current flowbetween said main anode and said cathode.

5. Discharge apparatus as in claim 4, wherein said closure meanscomprises a tube the lower end of which dips into the mercury heated bysaid heating means and which is apertured to permit flow of mercury tothe ignition space and emergence of the cathode spot therefrom.

6. Discharge apparatus as in claim 4, wherein said closure meanscomprises two tube sections loosely connected together the lower ofwhich dips into the mercury heated by said heating means, is pressedagainst the upper section by the upward thrust of the mercury, and isapertured to permit entrance of the mercury and exit of the cathodespot.

7. Discharge apparatus as in claim 4, wherein said closure meanscomprises a tube the lower end of which is provided with a funnel-shapedextension which dips into the mercury heated by said heating means fordirecting the vapor toward said ignition anode and is apertured topermit entrance of the mercury and exit of the cathode spot.

8. Discharge apparatus as in claim 4, wherein said heating means islocated in a metallic cap opening to the atmospheric side of saidcontainer.

9. Discharge apparatus as in claim 4, wherein said heating means islocated in a metallic cap opening to the atmospheric side of saidcontainer and is surrounded by a cylindrical tube element enclosing partof said mercury, extending beyond the surface thereof and being slottedto permit entrance of the mercury and exit of the cathode spot.

10. Discharge apparatus as in claim 4, wherein said ignition anode islocated in a tube projecting into said container through said cathodeand said closure means includes said tube and a hood dis-- posed overthe open upper end of said tube.

11. Discharge apparatus as in claim 4, wherein said heating meanscomprises a heating rod extending from the atmospheric side of saidcontainer into heat conductive relation to said cathode.

l2. Discharge apparatus as in claim 4, wherein said heating meanscomprises a space heater.

ARTHUR GAUDENZI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,242,786 Kingdon et al May 20,1941 1,032,914 Kruh July 16, 1912- 1,652,921 Wimberger Dec. 13, 19272,179,929 Hansell Nov. 14, 1939 FOREIGN PATENTS Number Country Date360,342 Great Britain Nov. 5, 1931 474,565 Great Britain Nov. 3, 193'?118,103 Switzerland Dec. 31, 1925 272,958 Great Britain Apr. 12, 1928

